Georeferenced map of Iceland Stretches

Question

I am trying to georeference a large map of iceland, and with every setting I try, the image streches out on the x axis. I have a feeling it has to do with coordnate projection, but I have tried everything I can think of (probably have tried at least 15 different crs). I have also tried every sampling method. What else can I try to make it more of a square image like shown below?

Try ISN2004 / Lambert 2004 https://epsg.io/5325 [5325 in QGIS] — Mapperz, Mar 30 '21 at 15:56
4326 will make the lines of longitude vertical rather than curved leading to the stretchign — Ian Turton, Mar 30 '21 at 16:08
Correct on 4326, that is the issue I am having. No luck with 5325, still looks stretched for me. I am including my settings if you see any issues. https://imgur.com/a/IyUbsVy — Jacob Benzaquen, Mar 30 '21 at 16:15

Babel · Accepted Answer · 2021-04-01T08:14:24.847

It is normal that your map looks streched: that what Island looks like if you set the project CRS to EPSG:4326 (check it with a basemap like OpenStreetMap). If you change the project CRS to another value (like WebMercator EPSG:3857), everything will be fine. Your "streched" georeferenced image will be transformed (again) to fit the project CRS. See here for details: https://gis.stackexchange.com/a/392388/88814

Georeferencing only makes sense when you use the image with a software that is spatially aware. Than, it does not play a role how your image looks like in a image viewing software as the raster will be anyhow distorted in a way to fit the CRS you set in your QGIS project. So first decide there which CRS you want to use for the project (maybe using a basemap to see how shapes are distorted) and than use the same CRS as output for the Georeferencer.

You might also want to use a local CRS: see https://epsg.io/?q=Iceland%20kind%3APROJCRS

Screenshot: I got acceptable results georefencing your image with 6 GCP-points and using Polynominal 2 transformation type and EPSG:3857: georeferenced image with OSM background map. If you change the project CRS to 4326, georeferenced image as well as OSM map will be "streched" as in your case, both both shapes will still fit :-)

Still giving me a "stretched" image, even with project and map crs set to 3857. I had o do it with poly1 as the polynomial 2 was giving me a "failed to transform gcp" error — Jacob Benzaquen, Mar 30 '21 at 17:31
How does your basemap looks like in 3857? Streched as well? It should look like above. — Babel, Mar 30 '21 at 17:49
Got it working by referencing using map canvas and base map rather than using the points on the map. Now to just get around the weird behavior in R. Thanks for your help! — Jacob Benzaquen, Mar 30 '21 at 18:53

Mapperz · Answer 2 · 2021-03-31T02:37:22.017

2

In Photoshop (or other image package) crop to the actual map export to tiff

In QGIS load the crop tiff into the georeferencer. Using Linear (to create a wordfile) 4 GCP points (make sure residual error is kept to a minimum)

georefence the tiff

reload into QGIS with the world file

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edited Mar 31 '21 at 02:37

answered Mar 30 '21 at 16:33

Mapperz

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Georeferenced map of Iceland Stretches

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